Diabetes mellitus is a disorder of carbohydrate metabolism, i.e. a syndrome characterized by hyperglycemia resulting from absolute or relative impairment in insulin secretion and/or insulin action.
Classification of Diabetes mellitus is based on the one adopted by the National Diabetes Data Group and WHO. Previously, it was based on age at onset, duration, and complications of the disease. Gestational diabetes mellitus is carbohydrate intolerance of variable severity with onset or first recognition during the current pregnancy. Patients with type I diabetes mellitus (DM), also known as insulin-dependent DM (IDDM) or juvenile-onset diabetes, may develop diabetic ketoacidosis (DKA). Patients with type II DM, also known as non-insulin-dependent DM (NIDDM), may develop nonketotic hyperglycemic-hyperosmolar coma (NKHHC). Common late microvascular complications include retinopathy, nephropathy, and peripheral and autonomic neuropathies. The most important clinical sequel of sensory loss is foot ulceration, the most common cause of hospital admission in diabetic patients and the leading cause of non-traumatic lower limb amputations (Boulton 1997, Jude 1999 and Cameron 2001). Macrovascular complications include atherosclerotic coronary and peripheral arterial disease.
Type I diabetes mellitus: Although it may occur at any age, type I diabetes mellitus most commonly develops in childhood or adolescence and is the predominant type of DM diagnosed before age 30. This type of diabetes accounts for 10 to 15% of all cases of DM and is characterized clinically by hyperglycemia and a propensity to diabetic ketoacidosis. The pancreas produces little or no insulin.
About 80% of patients with type I DM have specific HLA phenotypes associated with detectable serum islet cell cytoplasmic antibodies and islet cell surface antibodies (antibodies to glutamic acid decarboxylase and to insulin are found in a similar proportion of cases).
In these patients, type I DM results from a genetically susceptible, immune-mediated, selective destruction of >90% of their insulin-secreting cells. Their pancreatic islets exhibit insulitis, which is characterized by an infiltration of T lymphocytes accompanied by macrophages and B-lymphocytes and by the loss of most of the beta-cells, without involvement of the glucagon-secreting alpha-cells. The antibodies present at diagnosis usually become undetectable after a few years. They may be primarily a response to beta-cell destruction, but some are cytotoxic for beta-cells and may contribute to their loss. The clinical onset of type I DM may occur in some patients years after the insidious onset of the underlying autoimmune process. Screening for these antibodies is included in numerous ongoing preventive studies.
Type II diabetes mellitus: Type II DM is usually the type of diabetes diagnosed in patients >30 years, but it also occurs in children and adolescents. It is characterized clinically by hyperglycemia and insulin resistance. Diabetic ketoacidosis is rare. Although most patients are treated with diet, exercise, and oral drugs, some patients intermittently or persistently require insulin to control symptomatic hyperglycemia and prevent nonketotic hyperglycemic-hyperosmolar coma. The concordance rate for type II DM in monozygotic twins is >90%. Type II DM is commonly associated with obesity, especially of the upper body (visceral/abdominal), and often present after a period of weight gain. Impaired glucose tolerance associated with aging is closely correlated with the typical weight gain. Type II DM patients with visceral/abdominal obesity may have normal glucose levels after losing weight.
Type II DM is a heterogeneous group of disorders in which hyperglycemia results from both an impaired insulin secretory response to glucose and decreased insulin effectiveness in stimulating glucose uptake by skeletal muscle and in restraining hepatic glucose production (insulin resistance). However, insulin resistance is common, and most patients with insulin resistance will not develop diabetes, because the body compensates by adequately increasing insulin secretion. Insulin resistance in the common variety of type II DM is not the result of genetic alterations in the insulin receptor or the glucose transporter. However, genetically determined post-receptor intracellular defects likely play a role. The resulting hyperinsulinemia may lead to other common conditions, such as obesity (abdominal), hypertension, hyperlipidemia, and coronary artery disease (the syndrome of insulin resistance).
Genetic factors appear to be the major determinants for the development of type II DM, yet no association between type II DM and specific HLA phenotypes or islet cell cytoplasmic antibodies has been demonstrated. An exception is a subset of non-obese adults with detectable islet cell cytoplasmic antibodies who carry one of the HLA phenotypes and who may eventually develop type I DM.
Before diabetes develops, patients generally lose the early insulin secretory response to glucose and may secrete relatively large amounts of proinsulin. In established diabetes, although fasting plasma insulin levels may be normal or even increased in type II DM patients, glucose-stimulated insulin secretion is clearly decreased. The decreased insulin levels reduce insulin-mediated glucose uptake and fail to restrain hepatic glucose production.
Hyperglycemia may not only be a consequence but also a cause of further impairment in glucose tolerance in the diabetic patient (glucose toxicity) because hyperglycemia decreases insulin sensitivity and increases hepatic glucose production. Once a patient's metabolic control improves the insulin or hypoglycemic drug dose is usually lowered.
Some cases of type II DM occur in young, non-obese adolescents (maturity-onset diabetes of the young [MODY]) with an autosomal dominant inheritance. Many families with MODY have a mutation in the glucokinase gene. Impairments in insulin secretion and in hepatic glucose regulation have been demonstrated in these patients.
Insulinopathies are rare cases of DM, with the clinical characteristics of type II DM, result from the heterozygous inheritance of a defective gene, leading to secretion of insulin that does not bind normally to the insulin receptor. These patients have greatly elevated plasma immunoreactive insulin levels associated with normal plasma glucose responses to exogenous insulin.
Diabetes may also be attributed to pancreatic disease: Chronic pancreatitis; particularly in alcoholics, is frequently associated with diabetes. Such patients lose both insulin-secreting and glucagon-secreting islets. Therefore, they may be mildly hyperglycemic and sensitive to low doses of insulin. Given the lack of effective counter regulation (exogenous insulin that is unopposed by glucagon), they frequently suffer from rapid onset of hypoglycemia. In Asia, Africa, and the Caribbean, DM is commonly observed in young, severely malnourished patients with severe protein deficiency and pancreatic disease; these patients are not prone to diabetic ketoacidosis but may require insulin.
Diagnosis of diabetes mellitus: In a symptomatic patients, DM is established when the diagnostic criterion for fasting hyperglycemia is met: a plasma (or serum) glucose level of >=140 mg/dl (>=7.77 mmol/l) after an overnight fast on two occasions in an adult or child.
An oral glucose tolerance test may be helpful in diagnosing type II DM in patients whose fasting glucose is between 115 and 140 mg/dl (6.38 and 7.77 mmol/L) and in those with a clinical condition that might be related to undiagnosed DM (e.g. polyneuropathy, retinopathy).
Hyperglycemia is correlated to most of the microvascular complications of diabetes. It demonstrated a linear relationship between the levels of Hb A1c (see below) and the rate at which complications developed. Other studies have suggested that Hb A1c<8% is a threshold below which most complications can be prevented. Thus, therapy for type 1 DM should try to intensify metabolic control to lower Hb A1c while avoiding hypoglycemic episodes. However, treatment must be individualized and, should be modified when circumstances make any risk of hypoglycemia unacceptable (e.g. in patients with a short life expectancy and in those with cerebrovascular or cardiac disease) or when the patient's risk of hypoglycemia is increased (e.g. in patients who are unreliable or who have autonomic neuropathy).
Diet to achieve weight reduction is most important in overweight patients with type II DM. If improvement in hyperglycemia is not achieved by diet, trial with an oral drug should be started.
The patient should be regularly assessed for symptoms or signs of complications, including a check of feet and pulses and sensation in the feet and legs, and a urine test for albumin. Periodic laboratory evaluation includes lipid profile, BUN (blood urea nitrogen) and serum creatinine levels, ECG, and an annual complete ophthalmologic evaluation.
Hypercholesterolemia or hypertension increases the risks for specific late complications and requires special attention and appropriate treatment. Although beta-adrenergic receptor blocking agents (3-blockers, such as propranolol) can be used safely in most diabetics, they can mask the (3-adrenergic symptoms of insulin-induced hypoglycemia and can impair the normal counter regulatory response. Thus, ACE inhibitors and calcium antagonists are often used.
Plasma glucose monitoring should be carried out by all patients, and insulin-treated patients should be taught to adjust their insulin doses accordingly. Glucose levels can be tested with easy-to-use home analyzers using a drop of fingertip blood. A spring-powered lancet is recommended to obtain the fingertip blood sample. The frequency of testing is determined individually. Insulin-treated diabetic patients ideally should test their plasma glucose daily before meals, 1 to 2 hours after meals, and at bedtime.
Most physicians periodically determine glycosylated hemoglobin (Hb A1c) to estimate plasma glucose control during the preceding 1 to 3 months. Hb A1c is the stable product of non-enzymatic glycosylation of Hb by plasma glucose and is formed at rates that increase with increasing plasma glucose levels. In most laboratories, the normal Hb A1c level is about 6%; in poorly controlled diabetics, the level ranges from 9 to 12%. Hb A1c is not a specific test for diagnosing diabetes; however, elevated Hb A1c often indicates existing diabetes.
Another test determines the fructosamine level. Fructosamine is formed by a chemical reaction of glucose with plasma protein and reflects glucose control in the previous 1 to 3 weeks. Therefore, this assay may show a change in control before Hb A1c and is often helpful when intensive treatment is applied and in short-term clinical trials.
As regards insulin treatment, human insulin is often preferred in initiating insulin treatment because it is less antigenic than animal-derived varieties. However, detectable insulin antibody levels, usually very low, develop in most insulin-treated patients, including those receiving human insulin preparations.
Insulin is routinely provided in preparations containing 100 U/ml (U-100 insulin) and is injected subcutaneous with disposable insulin syringes. The ½-ml syringes are generally preferred by patients who routinely inject doses of <=50 U, because they can be read more easily and facilitate the accurate measurement of smaller doses. A multiple-dose insulin injection device (NovolinPen), commonly referred to as an insulin pen, is designed to use a cartridge containing several days' dosage.
Diabetes may be associated with other endocrine diseases. Type II DM can be secondary to Cushing's syndrome, acromegaly, pheochromocytoma, glucagonoma, primary aldosteronism, or somatostatinoma. Most of these disorders are associated with peripheral or hepatic insulin resistance. Many patients will become diabetic once insulin secretion is also decreased. The prevalence of type I DM is increased in patients with certain autoimmune endocrine diseases, e.g. Graves' disease, Hashimoto's thyroiditis, and idiopathic Addison's disease.
Diabetes may also be induced by beta-cell toxins. Streptozotocin for instance can induce experimental diabetes in rats but rarely causes diabetes in humans.
Adults with diabetes have an annual mortality of about 5.4% (double the rate for non-diabetic adults), and their life expectancy is decreased on average by 5-10 years. Although the increased death rate is mainly due to cardiovascular disease, deaths from non-cardiovascular causes are also increased. A diagnosis of diabetes immediately increases the risk of developing various clinical complications that are largely irreversible and are due to microvascular or macrovascular disease. Duration of diabetes is an important factor in the pathogenesis of complications, but other risk factors for example, hypertension, cigarette smoking, and hypercholesterolaemia interact with diabetes to affect the clinical course of microangiopathy and macroangiopathy.
One of the microvascular complications in diabetes is retinopathy. Diabetic retinopathy is a progressive disorder classified according to the presence of various clinical abnormalities. It is the commonest cause of blindness in people aged 30-69 years. Damage to the retina arises from a combination of microvascular leakage and microvascular occlusion; these changes can be visualized in detail by fluorescein angiography. A fifth of patients with newly discovered type 2 diabetes have retinopathy at the time of diagnosis. In type 1 diabetes, vision-threatening retinopathy almost never occurs in the first five years after diagnosis or before puberty. After 15 years, however, almost all patients with type 1 diabetes and two thirds of those with type 2 diabetes have background retinopathy.
Another microvascular complication in diabetes is nephropathy. Diabetic nephropathy is characterized by proteinuria >300 mg/24 h, increased blood pressure, and a progressive decline in renal function. At its most severe, diabetic nephropathy results in end stage renal disease requiring dialysis or transplantation, but in the early stages overt disease is preceded by a phase known as incipient nephropathy (or microalbuminuria), in which the urine contains trace quantities of protein (not detectable by traditional dipstick testing). Microalbuminuria is defined as an albumin excretion rate of 20-300 mg/24 h or 20-200 μg/min in a timed collection and is highly predictive of overt diabetic nephropathy, especially in type 1 diabetes.
The rate of decline in glomerular filtration rate varies widely between individuals, but antihypertensive treatment greatly slows the decline in renal function and improves survival in patients with diabetic nephropathy.
In patients with type I diabetes complicated by diabetic nephropathy, angiotensin converting enzyme inhibitors have renoprotective effects above those that can be attributed to reduced blood pressure; they are beneficial even in normotensive patients and ameliorate other associated microvascular complications such as retinopathy. In patients with type 2 diabetes, achieving good blood pressure control (which often requires combination therapy) is more important than the choice of antihypertensive drug, although angiotensin converting enzyme inhibitors are used as first line treatment.
Another microvascular complication in diabetes is polyneuropathy, being the major cause for foot ulcers and joint problems, which are important causes of morbidity in diabetes mellitus. In diabetic polyneuropathy, the sensory denervation impairs the perception of trauma from such common causes as ill-fitting shoes or pebbles. Alterations in proprioception lead to an abnormal pattern of weight bearing and sometimes to the development of Charcot's joints.
Patients with infected foot ulcers frequently feel no pain because of neuropathy and have no systemic symptoms until late in a neglected course. Deep ulcers and particularly ulcers associated with any detectable cellulites require immediate hospitalization, since systemic toxicity and permanent disability may develop. Early surgical debridement is an essential part of management, but amputation is sometimes necessary.
Interleukin-6 (IL-6) is a multifunctional cytokine produced and secreted by several different cell types. This pleiotropic cytokine plays a central role in cell defense mechanisms including the immune response, acute phase response and hematopoiesis. IL-6 is a 20 to 26 kDa glycoprotein having 185 amino acids that has been cloned previously (May et al, (1986); Zilberstein et al, (1986); Hirano et al, (1986)). IL-6 has previously been referred to as B cell stimulatory factor 2 (BSF-2), interferon-beta 2 and hepatocyte stimulatory factor. IL-6 is secreted by a number of different tissues including the liver, spleen, and bone marrow and by a variety of cell types including monocytes, fibroblasts, endothelial, B- and T-cells. IL-6 is activated at the transcriptional level by a variety of signals including viruses, double stranded RNA, bacteria and bacterial lipopolysaccarides, and inflammatory cytokines such as IL-1 and TNF.
The biological activities of IL-6 are mediated by a membrane receptor system comprising two different proteins one named IL-6 receptor or gp80 and the other gp130 (reviewed by Hirano et al, 1994). gp130 is a transmembrane glycoprotein with a length of 918 amino acids, including an intracellular domain of 277 amino acids, is a subunit constituent of several cytokine receptors, including those for IL-6, IL-11, LIF, Oncostatin M, CNTF (ciliary neurotrophic factor), CT-1. IL-6 being the prototype of the cytokines acting through gp130, this cytokine family is also called “IL-6 type cytokines”.
gp130 participates in the formation of high-affinity receptors for these cytokines by binding to low affinity receptor chains. Accordingly, gp130 has been called also an “affinity converter”. Ligand binding to a cytokine receptor leads to the dimerization of gp130 (shown for the IL-6 receptor) or heterodimerization (shown for LIF, Oncostatin M, and CNTF receptors) with a gp130-related protein known as the LIFRbeta subunit. Binding of the respective ligands is associated with the activation/association of a family of tyrosine kinases known as Janus kinases (JAKs), as the first step of intracellular signal transduction. Intracellular signaling processes include tyrosine phosphorylation and activation factors called STATs (signal transducer and activator of transcription).
The human gp130 gene product appears to be homologous to two distinct chromosomal loci on chromosomes 5 and 17. The presence of two distinct gp130 gene sequences is restricted to primates and is not found in other vertebrates.
It has been shown that the signaling activities of IL-6, IL-11, CNTF, Oncostatin M and LIF can be blocked specifically by different monoclonal antibodies directed against gp130. In addition to this, monoclonal antibodies, which directly activate gp130 independently of the presence of cytokines or their receptors have been found.
Other monoclonal antibodies directed against gp 130 have been shown to inhibit IL-6-mediated functions. Soluble forms of gp130 (sgp130) with molecular masses of 90 and 110 Kda have been found in human serum. They can inhibit biological functions of those cytokines utilizing receptor systems with gp130 as a component.
Soluble forms of IL-6R gp80 (sIL-6R), corresponding to the extracellular domain of gp80, are natural products of the human body found as glycoproteins in blood and in urine (Novick et al, 1990, 1992). An exceptional property of sIL-6R molecules is that they act as potent agonists of IL-6 on many cell types including human cells (Taga et al, 1989; Novick et al, 1992). Even without the intracytoplasmic domain of gp80, sIL-6R is still capable of triggering the dimerization of gp130 in response to IL-6, which in turn mediates the subsequent IL-6-specific signal transduction and biological effects (Muralcami et al, 1993). sIL-6R has two types of interaction with gp130 both of which are essential for the IL-6 specific biological activities (Halimi et al., 1995), and the active IL-6 receptor complex was proposed to be a hexameric structure formed by two gp130 chains, two IL-6R and two IL-6 ligands (Ward et al., 1994; Paonessa et al, 1995).
The circulating concentrations of sIL-6R (agonist) in normal subjects are relatively high and comparable to those of soluble gp130 (a natural antagonist of IL-6) of above 10 ng/ml (Corbi et al 2000 Eur J Cardiotherac Surg. 18 (1): 98-103, Disthabanchong et al. Clin Nephrol. 2002 October; 58(4):289-95). In contrast, the circulating concentrations of IL-6 are low about or below 10 pg/ml (Kado et al. 1999 Acta Diabetol. June 36 (1-2)67-72, Corbi et al 2000). Thus the effect of IL-6 administration in vivo, alone, without co-administration with sIL-6R in disease may or may not be effective and depends on the concentration of the soluble agonist/antagonist in a particular disease and in a particular location in the body.
Chimeric molecules linking the soluble IL-6 receptor and IL-6 together have been developed (Chebath et al. Eur Cytokine Netw. 1997 December; 8(4):359-65.). They have been designated IL-6R/IL-6. The chimeric IL-6R/IL-6 molecules were generated by fusing the entire coding regions of the cDNAs encoding the soluble IL-6 receptor (sIL-6R) and IL-6 (see FIG. 4). Recombinant IL-6R/IL-6 was produced in CHO cells (Chebath et al, Eur Cytokine Netw. 1997, WO99/02552). The IL-6R/IL-6 binds with a higher efficiency to the gp130 chain in vitro than does the mixture of IL-6 with sIL-6R (Kollet et al, Blood. 1999 Aug. 1; 94(3): 923-31).
IL-6 has been implicated in the pathogenesis of human inflammatory CNS diseases. Increased plasma and cerebrospinal fluid levels of IL-6 have been demonstrated in patients with multiple sclerosis (Frei et al., (1991)), for instance.
Recent experiments on the effects of IL-6 on cells of the central and peripheral nervous system indicate that IL-6 may have protective effects on neuronal cells as well as some impact on inflammatory neurodegenerative processes (Gadient and Otten, 1997, Mendel et al, 1998). IL-6 was found to prevent glutamate-induced cell death in hippocampal (Yamada et al., 1994) as well as in striatal (Toulmond et al., 1992) neurons. In transgenic mice expressing high levels of both human IL-6 and human soluble IL-6R (sIL-6-R), an accelerated nerve regeneration was observed following injury of the hypoglossal nerve as shown by retrograde labeling of the hypoglossal nuclei in the brain (Hirota et al, 1996). Furthermore, there has been some evidence that IL-6 is implied in a neurological disease, the demyelinating disorder Multiple Sclerosis (MS) (Mendel et al., 1998). Mice lacking the IL-6 gene were resistant to the experimental induction of MS. On the other hand, there have been reports indicating that IL-6 has a negative effect on neuronal survival during early post-traumatic phase after nerve injury (Fisher et al., 2001).
WO03033015 teaches the use of substances signaling through p130 such as IL-6, or an IL-6R/IL-6 chimera for the treatment and/or prevention of a specific type of neuropathy, diabetic neuropathy. In WO03033015 it was shown that the treatment with IL-6 prevented neural fibers from loss of the myelin sheath and degeneration.
As mentioned, it is well established that diabetes causes impaired nerve function. There are evidences that impaired nerve function is due to reduced nerve perfusion in diabetic patients. The latter is important for the etiology of diabetic neuropathy; several studies have shown that nerve conduction velocity deficits can be prevented or corrected by treatment with a variety of vasodilators including al-adrenoceptor antagonists, angiotensin AT1 antagonists and converting enzyme inhibitors, endothelin ETA antagonists, calcium channel blockers and nitrovasodilators [reviewed in Cameron et al 2001].
Contradictory results were published on the IL-6 vasomodulatory actions, for example, on in vivo studies reported by Baudry et al.(1996) exposure to IL-6 induced a significant dose-dependent vasoconstriction, while Minghini et al. (1998) reported on IL-6-induced vasodilatation.
As mentioned, patients with diabetes have large reduction in life expectancy and in quality of life due to diabetes-specific microvascular complications in the retina, renal glomerulus and peripheral nerve. Diabetes is the leading cause of blindness, end-stage renal disease and a variety of debilitating neuropathies. Diabetics are the fastest-growing group of renal dialysis and transplant recipients. Over 60% of diabetic patients suffer from neuropathy, which accounts for 50% of all non-traumatic amputations in the US.
Hyperglycaemia alone cannot completely explain the appearance of microvascular complications of diabetes since Intensive blood glucose control dramatically reduces microvascular complications, but does not prevent them altogether (Effect of intensive diabetes treatment on nerve conduction in the Diabetes Control and Complications Trial. Ann Neurol. 1995 December; 38(6):869-80 and Lancet 352:837-853.1998). The current optimal management of microvascular complications in diabetes can only attempt to control by controlling glycemia and then deal with the complications when they occur. Consequently, patients continue to go blind, develop renal failure, and undergo lower extremity amputations making a greater understanding of the pathogenesis of microvascular disease to enhance the development of rational therapies urgent (Cameron et al 2001).